Support exactOptionalPropertyTypes in TypeScript

[mrmckeb]

This is a quick change, and I'm happy to contribute.

When using TypeScript with exactOptionalPropertyTypes, we get errors because Segment types don't allow undefined to be supplied to optional values.

The fix is that whenever a type is optional, it should also allow undefined.

As an example:

export type TrackParams = {
  event: string
-  properties?: EventProperties
+  properties?: EventProperties | undefined
-  context?: ExtraContext
+  context?: ExtraContext | undefined
-  timestamp?: Timestamp
+  timestamp?: Timestamp | undefined
-  integrations?: Integrations
+  integrations?: Integrations | undefined
-  messageId?: string
+  messageId?: string | undefined
} & IdentityOptions

[silesky]

@mrmckeb makes sense, happy to accept a PR here. Thanks!

[mrmckeb]

I took a look at this and I see two options:

1. Codemod the whole codebase, so that every "optional" value accepts undefined - I have that mostly done, but it's a big PR.
2. Change only what we need, and over time, other people can create PRs if they find additional areas where they'd like to have undefined supported.

Either option will likely require more changes over time, as option 1 still won't prevent new code from being added that doesn't include undefined when the type is optional.

What do you think @silesky?

[silesky]

@mrmckeb -- definitely the one with the least amount of code changes, that ideally only touches the public APIs (i.e. Params). Thanks!

[mrmckeb]

Done - sorry it took so long @silesky!
#1156